In certain situations, it is useful to combine data signals received over plural channels from different sources. Those sources usually individually provide such signals at unpredictable times and immersed in background noise at a level close to that of the level of the data signals. Illustrative situations include seismic and sonar systems wherein masses of such data must be collected simultaneously from so many sources that it is burdensome for an individual operator to collate the data intelligently.
It is known to combine the signals from the respective channels onto a common output medium for monitoring. In the Tsuchiko U.S. Pat. No. 4,257,043, plural channel signals are combined as respective waveforms on a single cathode ray tube display. Combining by exclusive ORing is shown by W. A. Struzinski in "ORing Loss Data for Square Law Detectors Followed by an ORing Device and an Accumulator," Journal of the Acoustical Society of America, Vol. 72, No. 1, July 1982, pages 191-195. It has been found, however, that even after data is combined into a single output signal and displayed, it is sometimes difficult to evaluate because there is so much channel noise present that contrast is poor between the noise and the desired information signals.